Problem – Interface with microprocessor and write an assembly Subtract content of two ports by interfacing with microprocessor. The interfacing happens with the ports of the Microprocessor. The main IC’s which are to be interfaced with are: 1. PPI. 2. PIC. 3. USART. PPI: 82C55 The 82C55 is a popular interfacing component, that can interface any TTL-compatible I/O device to the microprocessor.

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Its not created and manipulated by a professional; But by a student like you. So there is chance of faults 82555 defects.

Looking forward for your comments and suggestions Other blogs of mine: Write a program to initialize in the configuration given below. Wlth a program to initialize in the configuration given below: Assume address of the control word register of as 83H. Assume address of the control word register of as 23H. Send it to control word register.

Design a system both Software and Hardware that will cause 4 LEDs to interfaxing 10 times when a push button switch is pressed. Assume persistence of vision to be 0. Load data to light LEDs. Send data on port C. Load data to switch off LEDs. Call Delay of 0. If not zero repeat. Jump back to read status. Design a microprocessor system to control traffic lights. The traffic light arrangement is as shown in Fig.

The traffic should be controlled in the following manner. Actual pin connections are listed in Table 1 below.

The electric bulbs are controlled by relays. The pins are used to control relay on-off action with the help of relay driver circuits. The driver circuit includes 12 transistors to drive 12 relays. Initializeport A and port B. Send data on PA to glow R1 and R2. Lnterfacing data on PB to glow G3 and G4. Send data on Port A to glow Y1 and Y2. Send data on port B to glow Y3 and Y4. Send data on port A to glow G1 and G2.

Send data on port B to glow R3 and R4. Send data on port A interfcing glow Y1 and Y2. Load count to give 0. Check whether count is 0. If not zero, repeat. Check if multiplier zero, otherwise repeat. Return to main program. Interface a Stepper Motor to the microprocessor system and write an assembly language program to control the Stepper Motor.


A stepper motor is a digital motor. It can be driven by digital signal. Motor shown in the circuit has two phases, with center-tap winding. The center taps of these windings are connected to the 12V supply.

Due to this, motor can be excited by grounding four terminals of the two windings. Motor can be rotated in steps by giving proper excitation sequence to these windings.

Microprocessors engineering – Interfacing the microprocessor

The intrfacing nibble of port A of the is used to generate excitation signals in the proper sequence. These excitation signals are buffered using driver transistors.

The transistors are selected such that they can source rated current for the windings. Motor is rotated by 1.

As port A is used as an output port, control word for is 80H. Stepper Motor Control Program: This is the code sequence for clockwise rotation. Get the Excite code. Interface an 8-digit 7 segment LED display using to the microprocessor system and write an assembly language routine to display message on the display. In this circuit port A and port B are used as simple latched output ports.

Port A provides the segment data inputs to the display and port B provides a means of selecting a display position at a time for multiplexing the displays.

A0-A7 lines are used to decode the addresses for For this circuit different addresses are: The register values are chosen in Fig. This current is required to produce an average of 10 mA per segment as the displays are multiplexed.

In this type of display system, only one of the eight display position is ‘ON’ at any given instant. Only one digit is selected at a time by giving low signal on the corresponding control line.

Load control word in AL. Load control word in CR. This “display message subroutine” must be called continuously to display the 7-segment coded message stored in the memory from address H. Interface an 8 x 8 matrix keyboard to through in 2-key lockout mode and write an assembly language program to read keycode of the pressed key.


Memory mapped I/O interfacing with 8085 microprocessor

The external clock frequency is 2MHz. Dont inteerfacing any Interrupts. The three steps needed to write the software are: Read FIFO status word. Mask bit B3 to B7. Initialize in read. In the interrupt driven mode interrupt line from is connected to the one of the interrupt input of except INTR.

Other signal connections are same as in the non interrupt mode. Find program clock command word. Load mask pattern to enable RST 7. Wait for the interrupt. Interrfacing in read FIFO.

Interface an 8 x 4 matrix keyboard to through Interfacing 8 x 4 keyboard matrix in decoded scan keyboard mode. As keyboard is having 8 rows and 4 columns, only 4 scan lines are required and we can avoid external decoder to generate scan lines by selecting decoded scan keyboard mode.

External clock frequency is 3 MHz. 82555 shown in the figure eight display lines Bo-B3 and Ao-A3 are buffered with the help of transistor and used to drive display digits.

These buffered lines are connected in parallel to all display digits. So, Sl and S2 lines are decoded and decoded lines are used for selection of one of the eight digits.

8255A – Programmable Peripheral Interface

To display 1 to 8 numbers on the eight 7-segment digits we have to load 7-segment codes for 1 to 8 numbers in the corresponding display locations. Find display RAM command word. Initialize lookup table pointer. Initial size in write Display. Get the 7-segment code. Write 7-segment code in display RAM. Increment lookup table pointer. Interface 4 x 4 matrix keyboard and 4 digit 7-segment display and write an tssembly language program to read keycode of the pressed key and display same key on: Here, 4 scan lines are sufficient to scan matrix keyboard and to select display digits.

Hence decoded mode is used. Initialize memory pointer to point. Initialize in write display RAM mode. Get the 7 segment code.

Source Program and Interrupt Service Routine. Write an assembly language program to roll message ‘HELL’ from right to left.